lo2k, from your post above i gather you were able to edit the jam, how ? what program, im still having no success, theres also the following:
targrey3.jam,wetfade.jam which might have some effect on mirrors,
i checked with filemon and all these jams do get loaded so i assume theyre used somewhere.
changing the jams also effects the track colour when bump mapping off, I think track surface is a combo of DPRD6.jam with either bump map or tarmacmap, depending weather you have bumpmapping selected or not.